A Population of Radio-loud Narrow Line Seyfert 1 Galaxies with Blazar-like Properties?

TL;DR

This study identifies a unique class of radio-loud NLS1 galaxies exhibiting blazar-like properties, suggesting they host relativistic jets and may represent a distinct population of AGN with moderate black hole masses and high accretion rates.

Contribution

It provides the first comprehensive analysis of radio-loud NLS1 galaxies with blazar-like features, proposing their potential as a new, distinct class of AGN with relativistic jets.

Findings

Radio-loud NLS1s show blazar-like radio and X-ray properties.

Many have relativistic jets indicated by VLBI and brightness temperatures.

Some resemble high-energy peaked BL Lacs in their spectral energy distributions.

Abstract

(abridged) We present a comprehensive study of a sample of 23 genuine radio-loud NLS1 galaxies which have the radio-loudness parameters greater than 100. The radio sources of the sample are ubiquitously compact. A significant fraction of these objects show interesting radio to X-ray properties that are unusual to most of the previously known radio-loud NLS1 AGN, but are reminiscent of blazars. These include flat radio spectra, large amplitude flux and spectral variability, compact VLBI cores, very high brightness temperatures derived from variability, enhanced optical emission in excess of the normal ionising continuum, flat X-ray spectra, and blazar-like SEDs. We interpret them as evidence for the postulated blazar nature of these very radio-loud NLS1 AGN, which might possess at least moderately relativistic jets. Intrinsically, some of the objects have relatively low radio power and would have been classified as radio-intermediate AGN. The black hole masses are estimated to be within 10^{6-8}Msun, and the inferred Eddington ratios are around unity. The results imply that radio-loud AGN may be powered by black holes with moderate masses (10^{6-7}Msun) accreting at high rates. We find that a significant fraction of the objects, despite having strong emission lines, resemble high-energy peaked BL Lacs (HBL) in their SED. Given the peculiarities of blazar-like NLS1 galaxies, questions arise as to whether they are plain downsizing extensions of normal radio-loud AGN, or whether they form a previously unrecognised population.